What Students Should Understand You can use a number line to count back to find the difference in a subtraction sentence.

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1 What's the Math? FOCUS Common Core State Standards Domain: Operations and Algebraic Thinking Major Cluster: Add and subtract within 20 Objective: Students will use a number line to count back to subtract. Standards 1.OA.5 Relate counting to addition and subtraction (e.g., by counting on 2 to add 2). Also addresses: 1.OA.6 Mathematical Practices 1 Make sense of problems and persevere in solving them. 2 Reason abstractly and quantitatively. 5 Use appropriate tools strategically. 6 Attend to precision. COHERENCE Thinking Across Grades Previous Grade K K.OA.2 Now Grade 1 1.OA.5 Linking to Major Topics Connected to the following critical area of focus: 1. Developing understanding of addition, subtraction, and strategies for addition and subtraction within 20. Connected to the following standards: K.OA.2, 1.OA.6, 1.OA.7, 2.OA.2 RIGOR The exercises increase in complexity throughout the lesson. However, individual student thinking may vary during extended processing. Levels of Complexity Level 1 Understand Concepts Exercises 1 4 Level 2 Apply Concepts Exercises 5 18 Level 3 Extend Concepts Exercises 19 20; Write Math Next Grade 2 2.OA.2 What Students Should Understand You can use a number line to count back to find the difference in a subtraction sentence. What Students Should Be Able To Do Students should be able to find the difference in a subtraction sentence by using a number line and counting back. 8 3 = 5 Building on the Essential Question In this lesson, students will build upon the skills and concepts needed to answer the chapter s Essential Printed by: Leah Duncan Page 1 of 11 Printed on 11/13/2014 2:32 PM

2 Question What strategies can I use to subtract? Printed by: Leah Duncan Page 2 of 11 Printed on 11/13/2014 2:32 PM

3 Developing Vocabulary / Get Ready Review Vocabulary/Cognate difference/diferencia number line/línea numérica Activity Have students point to the number line on the first page of the lesson. Ask students how a number line helps them add. Sample answer: It can help me see how many numbers I am counting on. Write 6 5 = on the board. Model how students could use the number line in the lesson to solve the subtraction number sentence. Attend to Precision Remind students that the answer, 1, is also known as a difference. English Language Learner Instructional Strategy Sensory Support: Act It Out Draw or display a large 0 12 number line. The number line should span across the front of the room as widely as possible. Have 11 large images of beach balls ready for this act it out activity. Say, A store has eleven beach balls to sell. Place the beach ball images above the numbers 1 through 11 on the number line. Say, It sells two of them. Have students count back from 11, ten, nine as you remove the beach balls on the numbers 11 and 10 on the number line. How many beach balls do they have left? nine Have students model using the paper clip on their number lines. Guide students through writing the number sentence. Ask, How many beach balls did the store have to sell? eleven Point to 11. Ask, How many beach balls did the store sell? two Point to 2. Ask, How many beach balls does the store have left? nine Write 9. Have students read the subtraction number sentence aloud. For non-spanish speaking ELLs, refer to the Multilingual eglossary for interactive definitions in 13 languages. My Vocabulary Cards Have students identify which of their vocabulary cards shows differences or number lines. Virtual Word Wall You may wish to add these review vocabulary words to the Virtual Word Wall for the chapter. Printed by: Leah Duncan Page 3 of 11 Printed on 11/13/2014 2:32 PM

4 Launch the Lesson / Investigate & Model Review Problem of the Day Ming needs 12 party hats for his party. He has 2 blue party hats and 5 green party hats. How many more party hats does he need? 5 hats Make Sense of Problems Have students explain the steps they used to solve this problem. Common Core Quick Check Use this activity as a quick review and assessment of the previous lesson. A printable version is available online. Additional review occurs at the end of the chapter. Additional Literature Connection Read a trade book, such as 12 Ways to Get to 11 by Eve Merriam, to prepare students for this lesson. Investigate the Math Target: Conceptual Understanding and Applications Materials: Lesson Presentation slides This investigation emphasizes mathematical reasoning. How can you use a number line to subtract? Students investigate ways to solve the problem using their model of choice. repeated reasoning. Model the Math Students come together to discuss their results and look for and express regularity in Target: Procedural Skill and Fluency Materials: Number Lines: Blank; to 20; to 100 by Fives from the Manipulative Masters, paper or plastic placemats, tape, connecting cubes Number and tape together sheets of paper or plastic placemats to create a large walk-on number line with numbers Give each student a number line from 0 to 20 and one connecting cube. Have a volunteer stand at the number 7 of the walk-on number line and take three steps back. Count back with students. Have students model counting back three from seven at their seats using their number line and cube. What subtraction number sentence shows what happened? 7 3 = 4 Repeat with other number combinations and volunteers. Printed by: Leah Duncan Page 4 of 11 Printed on 11/13/2014 2:32 PM

5 Printed by: Leah Duncan Page 5 of 11 Printed on 11/13/2014 2:32 PM

6 Teach Explore and Explain You will need: paper clips number line Introduce using a number line to subtract. Read the directions from the bottom of the student page. How many beach balls does the store have to sell? eleven beach balls Place a paper clip on that number on the number line. How many beach balls does the store sell? two beach balls Have students move the paper clip back that many spaces on the number line. Where is the paper clip now? on the nine So, how many beach balls does the store have left? nine beach balls Tell students to write the number on the line. Tell a number story that shows how many beach balls were sold, and how many are left at the store. Sample answer: Eleven beach balls minus two beach balls equals nine beach balls. Use Appropriate Tools Why is a number line helpful when you are subtracting? Sample answer: It shows the number I start at and the number I end at after I count back. See and Show Guide students through the example at the top of the page. Read the sentence to the class. Discuss how students can use the number line to help them subtract numbers. Explain to students to always start on the number line with the first number in the subtraction number sentence and count back by the second number in the number sentence. Have students trace the dashed number 6 to represent the difference of 9 3. Use Appropriate Tools Why do you move to the left on a number line when you are subtracting? When you subtract, the difference is smaller than the whole. The numbers are smaller when you move to the left on a number line. Work through Exercises 1 4 as a class. Talk Math: Collaborative Conversation Discuss with students Can you only use the number line to help you subtract numbers? Explain. Sample answer: No, you can also use a number line to help you add numbers. Persevere in Solving Problems Create a class Venn diagram that compares and contrasts using a number line to add and subtract. Printed by: Leah Duncan Page 6 of 11 Printed on 11/13/2014 2:32 PM

7 Practice & Apply On My Own Based on your observations, you may choose to assign exercises as noted in the levels below: Approaching Level Guide students through the exercises in On My Own. Help them to use manipulatives while working through the exercises. On Level Have students complete the exercises independently. Beyond Level Have students complete the exercises independently without using the number line. Common Error! Subtracting with a number line confuses some students. They might think: "I am on 10. I take away 2. I get rid of two numbers 9 and 8. That leaves 7." It is better for them to think: "I am on 10, and I am going to move back 2 steps. One step and I am on 9. Two steps and I am on 8." Problem Solving Attend to Precision Exercise 20 Ask students if it s possible to solve this version of the problem: 3 manatees are swimming near the shore. 5 of them swim away. How many manatees are still near the shore? Help them see that you cannot subtract a greater number than the whole. Make Sense of Problems Write Math When is it a good idea to use the strategy of subtracting on a number line? Sample answer: It is a good idea to use a number line to subtract when a small number is being subtracted. Formative Assessment Response Cards Read the following question aloud: The aquarium has 9 sharks in one tank. Another tank has 3 fewer sharks than the first tank. How many sharks are in the second tank? 6 sharks Have students write their answer with the unit on an index card. Have students turn in their response cards. Printed by: Leah Duncan Page 7 of 11 Printed on 11/13/2014 2:32 PM

8 Differentiated Instruction Differentiated Instruction TIER 2: Strategic Intervention Hands-On Activity Materials: inch ruler, 5 10 number cube, number cards 1 3; write-on/wipe-off board, dry erase marker Have students work in pairs. Place the number cards face down. The inch ruler will be used as a number line. One student rolls the number cube. The number that is rolled becomes the start number. Have the other student draw one card. The students count back 1, 2, or 3 from the start number, using the ruler as a number line. Students work together to write the matching number sentence on their board. TIER 1 Hands-On Activity Materials: number line 1 12, pencil, paper Invite partners to write subtraction sentences that start with the same number (between 7 and 12) and subtract 1, 2 and 3. For example, students will find 7 1; 7 2; and 7 3. Have students determine the pattern when subtracting 1, 2, and 3 from the same starting number. What happens on the number line each time you subtract? Sample answer: I move one number to the left when I subtract 1; I move two numbers to the left when I subtract 2; I move three numbers to the left when I subtract 3. Extend Hands-On Activity Materials: 0 12 number lines Challenge students to write counting-back riddles. Model with an example: I am the number 7. What is one way to find me on the number line? Sample answer: Count back 3 from 10. Have students write the number sentence that matches the riddle. Sample answer: 10-3 = 7. Have partners continue to trade and solve each other s riddles. Differentiated English Language Learner Support Act It Out Write the words difference and number line and their Spanish cognates, diferencia and linea numerica on a cognate chart. Create a 0 10 number line using a long piece of masking tape and students holding pieces of paper numbered 0 though 10. Say, The number line shows zero through ten. Write 8 2 =. Stand at 8. Take 2 large steps over to 6 as you, say, eight, seven, six. The difference is six. Repeat with exercises from the lesson using student volunteers to model counting back. Sentence Frames Printed by: Leah Duncan Page 8 of 11 Printed on 11/13/2014 2:32 PM

9 Place papers numbered 1 10 on the floor. Stand on 10 and step back two spaces, counting back as you go. Say, I started on ten. I counted back two. Now I am on eight. The difference is eight. Have a volunteer stand on 3. Say, Count back 2. Have the student use this sentence frame after moving back two spaces: I started on. I counted back. Now I am on. The difference is. Repeat the activity with different students and numbers. Number Game Distribute a 0 20 number line and a game piece to each student. Place students into groups of 3 and distribute a 3-part spinner numbered 1 through 3. All students place their game piece on 20 on the number line. Students take turns spinning a number. All group members count back that number on their number lines. With each subsequent turn, students continue counting back the number spun using the sentence frame: We start on and count back. We land on. The difference is. The first group to reach 0 wins. Printed by: Leah Duncan Page 9 of 11 Printed on 11/13/2014 2:32 PM

10 Wrap It Up My Homework Assign homework after successful completion of the lesson. Students who understand the concepts may skip the Homework Helper section. Problem Solving Reason Abstractly Exercise 12 Pair students and have them share which strategy they used to solve this problem. Is there more than one strategy that will work? See students' work. Test Practice Diagnose Student Errors Class trends in wrong answers may indicate common errors or misconceptions. 0 subtracted incorrectly 3 subtracted incorrectly 7 correct 8 subtracted incorrectly Formative Assessment You will need number line (0 12) Think-Pair-Share Invite partners to demonstrate subtracting 2 from 12 on a number line. Have students explain to their partner how they found the answer. Have students continue with explaining how to subract 1, 2 and 3 from other numbers on the number line. Invite a few pairs to share their conversation with the class. Printed by: Leah Duncan Page 10 of 11 Printed on 11/13/2014 2:32 PM

11 Printed by: Leah Duncan Page 11 of 11 Printed on 11/13/2014 2:32 PM